This invention relates to coils, such as ignition coils for spark ignition engines or any other high-voltage coil application, and, more particularly, to techniques for delivering the wire relative to a workpiece being wound to reduce wire slippage of a winding that may be wound using techniques generally referred in the art as bank, progressive, or pilgrim winding techniques.
It is known in the art of ignition systems for automotive applications to have an ignition coil that produces electromagnetic energy to create upon discharge a high voltage spark for initiating combustion in an engine cylinder. Typically, the ignition coil includes primary and secondary windings each wound around a bobbin or spool and disposed about a magnetic core. The foregoing description refers to ignition coils for automotive applications. However, the issues are also applicable to any high voltage coil for non-automotive, non-ignition applications.
The windings may be progressively wound around a receiving bobbin. As shown in FIG. 1, the winding equipment, e.g., a spindle drive 10 that may be mechanically coupled to a motor 11, presently requires the workpiece (e.g., the bobbin 12) to be wound to be held horizontally, with an incoming strand of wire 14, e.g., supplied by a wire feeder device 16, perpendicular relative to the horizontally positioned workpiece. With this winding technique, the strand of wire is wound to form a winding layer at an angle to reduce the number of turns between adjacent wires and thus keep the voltage potential low between two adjacent wires. One problem that may develop with this type of winding technique is wire slippage that may occur between wire layers wound around the coil bobbin, which could create an undesirable large voltage potential between adjacent wires, possibly resulting in arcing and/or electrical shorts. When wires are wound at an angle, the wires at the surface of the bobbin can slip and slide axially along the bobbin due to the tension and forces that may act on these wires.
FIG. 2 is an exemplary free body diagram corresponding to the winding technique of FIG. 1 illustrating the principal acting forces, which include force components along an orthogonal set of axes, e.g., X-Y axes. If there are residual force components not properly balanced along both the X and Y-axes, then wire slippage can occur. In the event slippage occurs, a new strand of wire will be wound on top of the slipped wire as the winding operation continues, resulting in a relatively high wire-to-wire voltage when the coil is operated. Thus, there is a need to provide improved winding techniques that would allow decreasing or avoiding wire slippage. This would allow suppliers, such as the assignee of the present invention, to maintain high quality and cost-effective progressive winding operations.